1. Field of the Invention
The present invention relates to an apparatus and a method for reproducing a surround wave field using wave field synthesis; and, more particularly, to an apparatus and a method for reproducing a surround wave field using wave field synthesis that can provide a constant sound image to a user, regardless of his position, for example, a vehicle riding position, and provide a wide listening space even in a limited space by localizing multi-channel audio signals at virtual sound images outside a narrow space to reproduce a surround wave field using particularly wave field synthesis (WFS) rendering, when reproducing the multi-channel audio signals through a loudspeaker array installed in the narrow space, for example, a vehicle space.
Though a vehicle space will be exemplified as a narrow space in the following embodiments, it should be noted that the present invention is not limited to the vehicle space.
This work was supported by the IT R&D program of MIC/IITA [2007-S-004-01, “Development of Glassless Single-User 3D Broadcasting Technologies”]
2. Description of Related Art
Audio reproduction methods extending from a typical stereo method to a method using a recent multi-channel audio format have been studied in various ways to improve a sound image localization function inside a vehicle.
Unbalance is generated from listener to listener due to a limited space of a vehicle even in these various methods. Since one listener is located close to a specific loudspeaker and another listener is located distant from the specific loudspeaker in a vehicle, the sound pressure of an audio signal can be differently delivered depending on each listener, and a time delay by distance occurs. That is, unbalance occurs due to different sound pressures or time delays depending on the positions of listeners inside the vehicle. The left and right balance of a sound pressure can be controlled to resolve this unbalance. However, the controlling of the left and right balance has an effect only one of passengers inside the vehicle and cannot resolve unbalance caused by time delay.
As a digital versatile disc (DVD) player is mounted in a vehicle recently, a reproduction signal changes from a stereo two-channel signal as in a compact disc (CD) into a multi-channel signal. Accordingly, an attempt to mount a plurality of loudspeakers inside the vehicle gradually increases.
Particularly, a center channel loudspeaker is most generally mounted. At this point, the loudspeaker installed in a position of a center fascia or a rearview mirror serves to form a center channel audio image to a listener. Also, a loudspeaker can be installed even in a backdoor of a vehicle to provide a better sound image to a listener sitting on a backseat.
FIG. 1 is an exemplary view of multi-channel loudspeakers installed in a conventional vehicle.
Multi-channel loudspeakers installed in the conventional vehicle are included in an audio reproduction system inside the vehicle. As illustrated in FIG. 1, the audio reproduction system installed inside the conventional vehicle reproduces audio signals using loudspeakers at a total of five positions, that is, a front left loudspeaker 101, a front right loudspeaker 102, a rear left loudspeaker 103, a rear right loudspeaker 104, and a sub woofer loudspeaker 105. At this point, the sub woofer loudspeaker 105 of the five loudspeakers serves to form a surrounding effect in an audio reproduction space non-directionally. Therefore, the sub woofer loudspeaker 105 has nothing to do with wave field reproduction.
The four loudspeakers 101 to 104 included in the audio reproduction system inside the vehicle are installed at the front left, front right, rear left, and rear right, respectively, so that the positions of physical sound images are fixed at the corresponding four positions.
Therefore, three-dimensional (3-D) audio reproduction technology is applied to the plurality of loudspeakers installed in the vehicle to reproduce a multi-channel audio signal. Multi-channel audio reproduction technology known up to now such as 5.1 channel surround or 7.1 channel surround, which is conventional 3-D audio reproduction technology provides a much better sound image than conventional stereo reproduction technology.
However, the conventional multi-channel audio reproduction technology provides better sound image only when a listener sits on the center of concentric circles along which the loudspeakers are arranged inside the vehicle. That is, the conventional multi-channel audio reproduction technology cannot provide an optimum sound image unless the listener is not positioned at the center of the concentric circles inside the vehicle. Meanwhile, a loudspeaker array can be provided to the front to reinforce a sound, but this method has nothing to do with a 3-D wave field reproduction.
In other words, conventional multi-channel audio reproduction technology is simple audio reproduction technology through a loudspeaker inside a vehicle and has a limitation of allowing a listener to feel a different sound image depending on the riding position of the listener due to a narrow listening space of a vehicle and the position of the loudspeaker to cause unbalance in audio reproduction, or not to provide a better sound image. Therefore, the conventional multi-channel audio reproduction technology has a limitation that a listener has a difficulty in overcoming a restriction of a narrow listening space of a vehicle.